AUTOMATIC FREQUENCY CONTROL CIRCUIT FOR FREQUENCY SHIFT KEYING RECEIVER

摘要

PROBLEM TO BE SOLVED: To allow a control circuit to have a provision for a frequency shift keying signal with a wide shift width without being affected by a content of a modulation code. ;SOLUTION: A frequency shift keying signal inputted to a frequency discriminator 5 is fed via a low pass filter 6 to a comparator 7, in which the signal is compared with an output from a reference voltage generator 8 and from which a rectangular wave is obtained. The comparator output is given to a clock recovery circuit 14 and a pulse generating circuit 16, from which a sampling pulse is obtained and the pulse is multiplied with the comparator output by a multiplier 13 and the product is converted into a DC voltage via a loop filter 12. The voltage denotes an error with respect to a reference shift width. The voltage is multiplied with the comparator output by a multiplier 11, from which a correction signal whose amplitude is the error voltage is obtained and fed to an adder/subtractor 10, in which the reference shift width is corrected. As a result, a frequency error signal whose shift width is corrected is obtained and the signal is used to control a VCO 19 via a loop filter 18 so as to correct a center frequency error.;COPYRIGHT: (C)1998,JPO